1. Field of the Invention
This invention relates to a valve apparatus for prevention of a shocking torque in a clutch mechanism. More particularly, the present invention relates to a valve apparatus for prevention of the shocking torque in the clutch mechanism of a vehicle.
2. Description of the Related Art
Referring to an operation of a manual transmission mounted on a vehicle, the manual transmission is initially disconnected from an engine by an operation of a clutch mechanism which is operated by a clutch pedal when a gear of the transmission is to be shifted. Later the transmission is connected with the engine by a release operation of the clutch mechanism after the gear is changed by an operation of a shift lever of the transmission. During operation of the transmission, a shocking torque is generated in the clutch mechanism by the rapid operation of the clutch mechanism when a difference between the rotation speed of the axles of the engine and the transmission is somewhat large. As a result of the shocking torque in the clutch mechanism, the engine is stopped, the vehicle is shocked and a clutch disk of the clutch mechanism is badly worn.
A conventional valve apparatus for prevention of the shocking torque in the clutch mechanism, which is disposed in a fluid conduit between a clutch master cylinder and a clutch release cylinder, is disclosed in the Japanese Patent Laid Open No. 4(1992)-145235. The valve apparatus disclosed in the prior art comprises a housing including a cylindrical chamber therein, a piston slidably disposed in the cylindrical chamber so as to partition the cylindrical chamber into a first chamber which is located near the master cylinder and a second chamber which is located near the release cylinder, a needle valve fixed to the housing and a spring forcing the piston toward the second chamber so that the piston is contacted with a plug which is fixed to the housing. The piston includes an opening connecting the first and second chambers. The needle valve extends through the opening so as to form a fluid passage between the needle valve and the opening. The passage has the largest sectional space when the piston is contacted with the plug. The farther the piston moves in the direction of the needle valve, the smaller the sectional space of the passage becomes. The valve apparatus further comprises a block mechanism. The block mechanism permits the piston to be slid toward the first chamber when the temperature of the fluid exceeds a predetermined value. On the other hand, the block mechanism prevents the piston from being slid farther than a value of the distance toward the first chamber when the temperature of the fluid is less than a value.
However referring to the valve apparatus of the prior art, the piston is directly forced by the fluid flowing into the second chamber when the fluid returns from the clutch release cylinder to the clutch master cylinder. Further the fluid passage of the valve apparatus is restricted relative to the fluid pressure which the piston receives. Therefore, variations in the viscosity of the fluid based on the temperature of the fluid and variations of a fluid speed based on a clutch pedal speed make it too difficult to provide the fluid passage with the required sectional space.